Approximately 90,000 known human proteins are the product of about 20,000 human genes. It is estimated that roughly 75% of human genes are subject to alternative splicing. Alternative splicing is the process responsible for this remarkable diversity of protein expression in general as well as tissue-specific expression of proteins. DNA is initially transcribed “literally” into pre-messenger RNA (pre-mRNA) comprising introns and exons. The average human protein coding gene is 28,000 nucleotides long with 8.8 exons separated by 7.8 introns. Exons are about 120 nucleotides long while introns are anywhere from 100-100,000 nucleotides long. Pre-mRNA is first processed by a spliceosome which recognizes where introns begin and end, removes introns, and joins exons together to form a mature mRNA that is then translated into a protein.
Pre-messenger RNA splicing is an essential process required for the expression of most genes. Improperly spliced mRNA molecules lead to altered proteins that cannot function properly, resulting in disease. Alternative splicing errors are known to contribute to cancer and many neurological diseases, including β-thalassemia, cystic fibrosis, spinal muscular atrophy (SMA), growth deficiencies, ataxia, autism, and muscular dystrophies.
5HT2CR: Prader-Willi syndrome (PWS)
Prader-Willi syndrome (PWS) is a genetic disorder caused by the deletion of paternal copies of several genes on the 15th chromosome located in the region 15q1-13 leading to deletion of a small nucleolar ribonucleoprotein (snoRNA), HBII-52. Deletion of the same region on the maternal chromosome causes Angelman syndrome. The incidence of PWS is about 1 in 12,000 to 1 in 15,000 live births. Phenotypically, individuals afflicted with PWS typically exhibit significant cognitive impairment, hyperphagia often leading to morbid obesity, an array of compulsive behaviors, and sleep disorders.
After transcription, nascent or pre-mRNA undergoes a series of processing steps in order to generate a mature mRNA molecule. snoRNAs are non-protein coding RNAs that are 60-300 nucleotides (nt) long and that function in guiding methylation and pseudouridylation of ribosomal RNA (rRNA), small nuclear RNAs (snRNAs), and transfer RNAs (tRNAs). Each snoRNA molecule acts as a guide for only one (or two) individual modifications in a target RNA. In order to carry out the modification, each snoRNA associates with at least four protein molecules in an RNA/protein complex referred to as a small nucleolar ribonucleoprotein (snoRNP). The proteins associated with each RNA depend on the type of snoRNA molecule incorporated. The snoRNA molecule contains an antisense element (a stretch of 10-20 nucleotides) which are complementary to the sequence surrounding the nucleotide targeted for modification in the pre-RNA molecule. This enables the snoRNP to recognise and bind to the target RNA. Once the snoRNP has bound to the target site the associated proteins are in the correct physical location to catalyse the chemical modification of the target base.
The two different types of RNA modification (methylation and pseudouridylation) are directed by two different families of snoRNAs. These families of snoRNAs are referred to as antisense C/D box and H/ACA box snoRNAs based on the presence of conserved sequence motifs in the snoRNA. There are exceptions, but as a general rule C/D box members guide methylation and H/ACA members guide pseudouridylation. HBII-52, also known as SNORD115, belongs to the C/D box class of snoRNAs.
In the human genome, HBII-52 is encoded in a tandemly repeated array with another C/D box snoRNA, HBII-85, in the Prader-Willi syndrome (PWS) region of human chromosome 15q1-13. This locus is maternally imprinted, meaning that only the paternal copy of the locus is transcribed.
The snoRNA HBII-52 is exclusively expressed in the brain and is absent in PWS patients. HBII-52 lacks any significant complementarity with ribosomal RNAs, but does have an 18 nucleotide region of conserved complementarity to exon 5 of serotonin 2C receptor (5-HT2CR) pre-mRNA. snoRNA HBII-52 is an example of an RNA that regulates pre-mRNA splicing by binding to a splice suppressor sequence of the 5-HT2CR gene, resulting in enhancement of exon 5b inclusion and the expression of a full-length, functional 5-HT2C receptor.
A recent study showed that these sequences co-varied among species, such that differences in nucleotides in one were always matched by complementary changes in the other; so that 100% complementarity is always present (Kishore and Stamm, 2006, Science 311:230-232). Kishore and Stamm, 2006, Science 311:230-232 also used a minigene construct to demonstrate that interaction of 5-HT2CR and HBII-52 at the consensus sequences is critical for appropriate splicing of the 5b exon so that a functional receptor is generated. When HBII-52 is mutated at sites that prevent its interaction with 5-HT2C, exon 5a is included and exon 5b is excluded. The splice variant containing 5a leads to a nonfunctional, out of frame, truncated transcript (Kishore and Stamm, 2006, Science 311:230-232).
Dysregulation of serotonergic systems appears to play a role in many cognitive disorders, including depression, autism, and obsessive compulsive disorder. Although a direct link between dysfunction of 5-HT2CR and PWS has yet to be demonstrated, 5-HT2CR knockout mice display phenotypic characteristics that are remarkably similar to those observed in PWS, including development of hyperphagia-induced obesity. In patients with PWS, satiety centers seem to be perturbed, leading to excessive overeating and obesity. Similarly, in 5-HT2C receptor knockout mice, obesity develops due to a lack of control of feeding behavior (Nonogaki et al., 1998, Nature Med. 4:1152-1156). 5-HT2CR agonists appear to be effective in inducing satiety (Nilsson, 2006, J. Med. Chem. 49:4023-4034). Another notable characteristic of patients with PWS is compulsive behavior. 5-HT2CR knockout mice also demonstrate compulsive-like behavior (Chou-Green et al., 2003, Physiol. Behav. 78:641-649). Interestingly, 5-HT2CR agonists are effective in animal models of obsessive-compulsive disorder (OCD); suggesting dysfunction of this receptor system could play a role in this disorder (Jenck et al., 1998, Expert. Opin. Invest. Drugs 7:1587-1599; Dunlop et al., 2006, CNS Drug Rev. 12:167-177). The sleep impairment observed in many PWS patients is also found in the 5-HT2CR knockout mouse (Frank et al., 2002, Neuropsychopharmacology 27:869-873). These mice also exhibited reduced hippocampal-dependent learning and deficits in hippocampal synaptic plasticity that appears to be critical in learning and memory (Tecott et al., 1998, Proc. Natl. Acad. Sci. 95:15026-15031). Thus 5-HT2C receptor knockouts may replicate some of the cognitive deficits found in PWS. 5-HT2CR knockout mice therefore share many, but not all (e.g., failure to thrive, which may be mediated by HBII-85 (Ding et al., 2005, Mamm. Genome 16:424-431)), critical phenotypes with PWS patients.
AMPA Receptor: Excitotoxicity, Seizure, and Amyotrophic Lateral Sclerosis (ALS)
The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (also known as AMPA receptor, AMPAR, or quisqualate receptor) is a non-NMDA-type ionotropic transmembrane receptor for glutamate in the central nervous system (CNS). Postsynaptic ion channels activated by glutamate include NMDA (N-methyl-D-aspartic acid)-type glutamate channels, which are highly Ca2+ permeable, and AMPA-type glutamate channels, which mediate the majority of rapid excitatory neurotransmission. AMPA channels are homo- or hetero-oligomeric assemblies composed of various combinations of four possible subunits, GluR1, GluR2, GluR3 and GluR4. The Ca2+ conductance of AMPA receptors differs markedly according to whether the GluR2 subunit is present or not and whether it has undergone post-transcriptional RNA editing at the Q/R site. AMPA receptors that contain at least one Q/R edited GluR2 subunit are Ca2+ impermeable. These properties of GluR2 are generated by RNA editing at the Q/R site in the putative second transmembrane domain (M2), during which a glutamine (Q) codon is replaced by an arginine (R) codon (Seeburg et al., 2001, Brain Res. 907:233-243). It is thought that arginine in the pore of the channel impedes Ca2+ permeation. Analyses of adult rat, mouse, and human brains have demonstrated that almost all GluR2 mRNA in neurons is edited. In contrast, the Q/R site of GluR1, GluR3 and GluR4 subunits are always unedited, and glutamine remains at this crucial position. Therefore, AMPA receptors lacking a Q/R edited GluR2 subunit or lacking GluR2 altogether are highly Ca2+ permeable (Kawahara and Kwak, 2005, ALS Other Motor Neuron Disord 6:131-144; Seeburg et al., 2001, Brain Res. 907:233-243).
Alternative splicing of the GluRs plays a critical role in AMPA receptor physiology, influencing sensitivity to glutamate, kinetics of channel desensitization, and intracellular trafficking. Two specific alternatively spliced variants of all GluRs called “flip” and “flop” are normally expressed in the CNS. These consist of 115 base pair exons that constitute the flip/flop cassette (Sommer et al., 1990, Science 249:1580-1585) and encode part of the extracellular segment that precedes the fourth transmembrane domain. This domain appears to modulate receptor desensitization and channel conductance (Mosbacher et al., 1994, Science 266:1059-1062). Generally, the AMPA “flip” variants are resistant to desensitization, whereas the “flop” variants are readily desensitized, although the kinetic difference depends on the subunit and, for heteromeric channels, on subunit compositions (Grosskreutz et al., 2003, Eur. J. Neurosci. 17:1173-1178; Koike et al., 2000, J. Neurosci. 25:199-207; Mosbacher et al., 1994; Sommer et al., 1990, Science 249:1580-1585). The extracellular flip/flop region may also interact with ER luminal proteins to regulate trafficking of AMPA receptors, with flip isoforms inserted into the cell membrane and flop isoforms trapped internally (Coleman et al., 2006, J. Neurosci. 26:11220-11229), although this has yet to be confirmed in neurons. Together these data show that when flip/flop ratio of GluR1, GluR3 and GluR4 is elevated, neurons are more excitable and show greater Ca2+ conductance.
In motor neurons (MNs) it has been consistently demonstrated that AMPA receptor desensitization significantly impacts the shape of the glutamatergic synaptic response, as well as robustly regulating network activity (Ballerini et al., 1995, Eur. J. Neurosci. 7:1229-1234; Funk et al., 1995, J. Neurosci. 15:4046-4056). In addition, studies in several different brain regions have found that AMPA receptor desensitization has potent effects on baseline evoked and spontaneous synaptic events (Akopian and Walsh, 2007, J. Physiol. 580:225-240; Atassi and Glavinovic, 1999, Pflugers Arch. 437:471-478; Xia et al., 2005, J. Pharmacol. Exp. Ther. 313:277-285), although this is controversial, especially in hippocampus (Arai and Lynch, 1998, Brain Res. 799:230-234; Hjelmstad et al., 1999, J. Neurophysiol. 81:3096-3099). Further, AMPA receptor desensitization has been shown to be critical in shaping the synaptic response under conditions of higher frequency activity by strongly regulating synaptic integration (Arai and Lynch, 1998, Brain Res. 799:235-234; Chen et al., 2002, Neuron 33:779-788). Prolonging AMPA channel desensitization can also generate excessive network synchronization, leading to paroxysmal bursting that may interfere with normal network function (Funk et al., 1995, J. Neurosci. 15:4046-4056; Pelletier and Hablitz, 1994, J. J. Neurophysiol. 72:1032-1036; Qiu et al., 2008, J. Neurosci. 28:3567-3576). Thus, it is not surprising that reducing AMPA receptor desensitization profoundly increases excitotoxicity induced by glutamate and AMPA.
In spinal MNs, as well as in hippocampus and cerebellar granule cells, treatment with AMPA alone does not induce neurotoxicity. However, AMPA combined with cyclothiazide, which greatly reduces AMPA receptor desensitization, leads to neuronal cell death (Carriedo et al., 2000, J. Neurosci. 20:240-250; May and Robison, 1993, J. Neuroschem. 60:1171-1174; Puia et al., 2000, Prog. Neuropsychopharm. Biol. Psychiatr. 24:1007-1015). AMPA-mediated neurotoxicity is also amplified by cyclothiazide in cerebellar purkinje cells (Brorson et al., 1995, J. Neurosci. 15:4515-4524) and cortical neurons (Jensen et al., 1998, Neurochem. Int. 32:505-513). Further, in HEK293 cells, AMPA induces excitotoxicity when flip but not flop GluR isoforms are expressed (Iizuka et al., 2000, Eur. J. Neurosci. 12:3900-3908). AMPA receptor desensitization can also protect against NMDA receptor mediated excitotoxicity (Jensen et al., 1998, Neurochem. Int. 32:505-513; Zorumski et al., 1990, Neuron 5:61-66). Finally, decreases in AMPA receptor desensitization have been proposed to play a role in excitotoxicity after traumatic brain injury (Goforth et al., 1999, J. Neurosci. 19:7367-7374). Thus, AMPA receptor desensitization plays a critical role in normal neuronal function and excitotoxicity.
Emerging evidence supports the idea that Ca2+-permeable AMPA channels, which are highly expressed on MNs, are key contributors to injury of MNs in amyotrophic lateral sclerosis (ALS) (Corona et al., 2007, Expert Opin. Ther. Targets 11:1415-1428; Van Den et al., 2006, Biochem. Biophys. Acta. 1762:1068-1082). Compared to most cell types, MNs have relatively poor capacity to buffer Ca2+, due to reduced levels of Ca2+ binding proteins including calbindin and parvalbumin (Alexianu et al., 1994, Ann. Neurol. 36:846-858; Ince et al., 1993, Neuropathol. Appl. Neurobiol. 19:291-299; Palecek et al., 1999, J. Physiol. 520 pt 2: 485-502). It appears that spinal MNs of ALS mice have even fewer of these Ca2+-binding proteins (Siklos et al., 1998, J. Neuropathol. Exp. Neurol. 57:571-587). Amplifying that point, recent studies have shown that G93A ALS mice interbred with mice overexpressing parvalbumin showed a delayed onset of motor disease (Beers et al., 2001, J. Neurochem. 79:499-509). According to a speculative model of glutamate-mediated excitotoxicity involving AMPA channels in ALS, Ca2+ influx through Ca2+-permeable AMPA channels is not adequately buffered in MNs and ends up accumulating in mitochondria. High Ca2+ is toxic to mitochondria, causing generation of apoptotic mediators such as ROS and cytochrome c, as well as opening of a permeability transition pore through which apoptotic mediators are released. It is thought that these mitochondrial factors are released from MNs and exert deleterious effects on glutamate transporters on adjacent astrocytes. Astrocytic glutamate transporters are responsible for taking up synaptic glutamate, and when they are compromised, glutamate accumulates in the synaptic region. The glutamate transporter with the most functional significance in this context is EAAT2/GLT-1, as it is widely expressed in astrocytes throughout the CNS and as it has the highest affinity for glutamate. In over ˜65% of ALS cases, and in ALS mice, EAAT2 activity in the cortex and spinal cord is compromised (Van Den et al., 2006, Biochem. Biophys. Acta. 1762:1068-1082). Thus, in this model, increased glutamate then further stimulates more Ca2+ influx though AMPA channels causing a feed-forward cycle that ultimately leads to too much Ca2+ in MNs. This sets into motion a cascade that leads by unknown mechanisms to MN cell death.
There is also evidence that decreased desensitization of AMPA channels, due to increased flip/flop expression ratio, may exacerbate glutamate excitotoxicity in ALS. In spinal MNs of ALS subjects, the level of the AMPA receptor flip variants was found to be significantly elevated relative to that of the flop isoforms (Tomiyama et al., 2002, Synapse 45:245-249). Although this work from a highly published neuroanatomy group is the only study thus far to examine flip/flop isoforms in spinal cord of ALS patients, the findings were quite compelling. They observed a 41-66% decrease in the flop isoforms of GluR1-3 only in the ventral horn (layer IX), where MN soma are localized. Further, they provided evidence that their transcript labeling was restricted to MN soma. Unfortunately, flip/flop protein levels were not examined, since specific antibodies for flip and flop isoforms of GluRs do not exist. A remarkably similar change in AMPA receptor flip/flop ratios was independently observed in MNs from G93A SOD1 ALS mice (Spalloni et al., 2004, Neurobiol. Dis. 15:340-350). This study showed increased flip isoforms, especially GluR3 and GluR4, and thus dramatic increases in flip to flop ratios. Interestingly, these changes were specific to mice overexpressing mutant SOD1 but were not found in mice overexpressing normal human SOD1. Further, electrophysiological studies demonstrated reduced desensitization of AMPA currents in MNs of G93A transgenics compared to control and SOD1 transgenics, as well as robust increases in blockade of desensitization by cyclothiazide. Both of these properties are characteristic of increased flip isoforms (Partin et al., 1994, Mol. Pharm. 46:129-138; Sommer et al., 1990, Science 249:1580-1585). In addition, spontaneous glutamatergic synaptic events are prolonged due to increased decay times in MNs of G93A ALS mice compared to control and SOD1 transgenics, also consistent with an increase in flip isoforms (Pieri et al., 2003, Neurosci. 122:47-58). Together, these studies indicate that aberrant flip-flop ratios are present in MNs of ALS individuals, and that these changes are replicated in a mouse model of the disease. These data strongly implicate a contribution of aberrant flip-flop levels of AMPA channels to MN excitotoxicity in ALS. Specifically, MNs with high levels of Ca2+-permeable AMPA receptors (Kawahara et al., 2004, Nature 427:801), and especially membrane bound non-desensitizable flip isoforms, permit enhanced postsynaptic Ca2+ influx in response to a given glutamate load (FIG. 2).
Increases in the flip to flop ratio in adult hippocampus have also been reported after seizures. This recapitulation of the immature phenotype after seizures is seen for many other neurotransmitter related proteins (Brooks-Kayal et al., 1998). In rat hippocampus, the flip variant of both GluR1 and GluR2 is increased after seizures induced by tetanus toxin (Rosa et al., 1999, Epilepsy Res. 36:243-251) and kindling (Kamphuis et al., 1992, Neurosci. Lett. 148:51-54; Kamphuis et al., 1994, nature 448:39-43). In hippocampal tissue from humans with epilepsy, increases in flip-flop ratios have also been reported. The GluR1 flip variant is increased in hippocampal astrocytes, as assessed both functionally with electrophysiology and at the transcript level with single-cell real time PCR (Seifert et al., 2004, J. Neurosci. 24:1996-2003). In hippocampal neurons, expression of the GluR1 flip variant is increased in CAl after seizures (Eastwood et al., 1994, Neuroreport 5:1325-1328; de Lanerolle et al., 1998, Eur. J. Neurosci. 10:1687-1703). While the flop variant is found in CA3 and dentate in non-epileptic hippocampus (Eastwood et al., 1994, Neuroreport 5:1325-1328), in tissue from patients with TLE the flop variant of GluR1 is found only in the dentate (de Lanerolle et al., 1998, Eur. J. Neurosci. 10:1687-1703). Thus flop appears to be downregulated in CA3 in epileptic hippocampus. The increase in flip to flop ratios in epileptic hippocampus would increase synaptic gain and could contribute to post-seizure hyperexcitability.
Aph1B: Alzheimer's Disease
Alzheimer's Disease (AD) is a common neurodegenerative disorder and results in a severe decline in cognition, and ultimately dementia, especially in the aged population. Progression of the disease is linked to the characteristic deposition of β-amyloid and tau neurofibrillary tangles (NTs).
Compelling evidence shows that amyloid-beta peptide (Aβ) contributes to the etiology of AD. Aβ is a 38-43 amino acid peptide that is produced in neurons by the sequential proteolytic cleavage of APP by β-secretase and γ-secretase, the latter step yielding isoforms Aβ40 and Aβ42. Aβ42 appears to be the most highly amyloidogenic isoform. In humans, γ-secretase complexes are heterogeneous, comprised of two presenilin genes (PS1 and PS2), along with Aph1A (long or short isoforms) and Aph1B (Shirotani et al., 2004, J. Biol. Chem. 279:41340-41345).
Gamma-secretase is a tri-partite protein complex composed of presenilin, nicastrin, and ApH1. ApH1 is composed of both Aph1A and Aph1B. Transgenic elimination of Aph1B blocked the processing of amyloid precursor protein (APP) to A-beta, but did not effect the processing of other non-amyloidal substrates (Semeels et al., 2009, Science 324:639-642).
A common understanding about AD is that APP processing sequentially by BACE then gamma-secretase, results in the production of Abeta42 among other isoforms. The Abeta42 isoform, which is the direct product of gamma-secretase cleavage is thought to be especially harmful, first as a soluble factor that impairs cognition and later in the production of amyloid plaques that may further enhance disease progression. Therefore, an intense search for compounds that reduce the activity of gamma-secretase is underway. Unfortunately, in addition to actively cleaving APP, gamma-secretase also cleaves a number of other important non-amyloidal substrates, such as Notch. Thus, there is an urgent need for improved compounds that significantly reduce gamma-secretase production of Aβ-42 in the brain, without affecting its cleavage of other non-APP substrates.
O-GlcNAcase (OGA): Alzheimer's Disease
Levels of N-acetyl-D-glucosamine (O-GlcNAc) modification of proteins are known to be reduced throughout the brains of Alzheimer's Disease (AD) patients due to low glucose availability, and this global alteration is thought to be pathological in AD progression (Fischer, 2008, Nature Chem. Biol. 4:448-449). Dynamic cycling of O-GlcNAc is regulated by addition through N-acetyl-D-glucosamine polypeptidyltransferase (OGT) and removal by O-GlcNAcase (OGA). Removal of O-GlcNAc from proteins by OGA may be involved in controlling multiple cellular pathways. OGA has been shown to mediate transcriptional activation both by directly modifying the transcriptome and by preventing the recycling of transcription factors in the nucleus (Bowe et al., 2006, Mol. Cell Biol. 26:8539-8550). Additionally, OGA has been implicated in chromatin remodeling and transcriptional repression via interactions with OGT/histone deacetylase (HDAC) complexes and or C-terminal histone acetyltransferase (HAT) activity (Lazarus et al., 2009, Int. J. Biochem. Cell Biol. 41:2134-2146; Whisenhunt et al., 2006, Glycobiol. 16:551-563). There is also evidence that phosphorylation and O-GlcNAcylation exist in dynamic equilibrium. Serine/threonine residues that otherwise may be phosphorylated by serine/threonine kinases can be instead O-GlcNAc modified, as is the case with tau (Yuzwa et al., 2008, Nat. Chem. Biol. 4:483-490). Further evidence indicates that O-GlcNAcylation of tau can cause trafficking and retention of tau in the nucleus (Guinez et al., 2005, Int. J. Biochem. Cell Biol. 37:765-774) Importantly to AD pathology, low levels of O-GlcNAc on tau may allow for tau hyperphosphorylation, which leads to neurofibrillary tangle (NT) formation. Thus alteration of brain glycosylation will have effects on multiple pathways.
HER3: Cancer
About 25% of breast cancers involve overexpression of the HER2, with highly aggressive metastasis, and poor clinical prognosis. Herceptin shows some success against HER2 overexpressing breast cancer cells (HOBCsa), and tyrosine kinase inhibitors (TKIs) have shown promise in early clinical trials. However, HOBCs show remarkable acquired resistance to current drugs. Recent studies have shown HER3 is overexpressed in HOBCs and exerts a critical role in tumorogenesis, metastasis, and acquisition of resistance to TKIs (Baselga, J. & Swain, S. M. (2009) Novel anticancer targets: revisiting ERBB2 and discovering ERBB3. Nat Rev Cancer 9:463-475). For EGFRs, dimerization and transactivation by tyrosine kinase is essential for signaling activity. Although HER3 lacks intrinsic tyrosine kinase activity, the most potent EGFR activated dimers are heterodimers between HER2 and HER3, leading to potent HER3-mediated TKI resistance via activation of the PI3K-Akt pathway (Baselga et al., 2009, Nat Rev Cancer 9:463-475). Since the loss of HER3 function ameliorates the transforming capabilities of HER2, there is a pressing need for new drugs against HER3 for treating breast cancer.
Forkhead Box Protein M1 (FOXM1): Anti-tumor
Forkhead box protein M1 (FOXM1) is a protein that is encoded by the FOX1 gene and is a member of the FOX family of transcription factors. FOXM1 is known to play a key role in cell cycle progression. There are three FOXM1 isoforms, A, B and C. Isoform FOXM1A has been shown to be a gene transcriptional repressor whereas the remaining isoforms (B and C) are both transcriptional activators. Hence, it is not surprising that FOXM1B and C isoforms have been found to be upregulated in human cancers (Wiestra et al., 2007, Biol. Chem. 388 (12): 1257-74.
The exact mechanism of FOXM1 in cancer formation remains unknown. It is thought that upregulation of FOXM1 promotes oncogenesis through abnormal impact on its multiple roles in cell cycle and chromosomal/genomic maintenance.
FOXM1 overexpression is involved in early events of carcinogenesis
FOXM1 gene is now known as a human proto-oncogene. Abnormal FOXM1 upregulation was subsequently found in the majority of solid human cancers including liver (Teh et al., 2002, Cancer Res. 62: 4773-80) breast (Wonsey et al., 2005, Cancer Res. 65 (12): 5181-9), lung (Kim et al., 2006, Cancer Res. 66 (4): 2153-61), prostate (Kalin et al., 2006, Cancer Res. 66 (3): 1712-20; cervix of uterus (Chan et al., 2008, J. Pathol. 215 (3): 245-52), colon (Douard et al., 2006, Surgery 139 (5): 665-70), pancreas (Wang et al., 2007, Cancer Res. 67 (17): 8293-300), and brain (Liu et al., 2006, Cancer Res. 66 (7): 3593-602).
Cyclophilin D: ALS, Hepatitis B Viral Infection, and Liver Cancer
Cyclophilin D (CypD) is a protein located in the matrix of the mitochondria, and is one of the components of the mitochondrial permeability transition pore (MPTP). Under conditions of oxidative stress, the MPTP becomes extremely permeable to the influx of calcium ions, therein causing mitochondrial swelling eventually leading to cell apoptosis. Targeting the MPTP/CypD complex in hepatitis B virus (HBV) infected hepatocytes using the non-specific CypD inhibitor, Cyclosporin A, inhibits HBV replication (Waldemeier et al., 2003, Current Medicinal Chemistry 10:1485-1506). In addition, when used in patients with neurodegerative diseases, Cyclosporin A exhibits cytoprotective effects by way of blocking the opening of the MPTP. Although shown to be efficacious, Cyclosporin A is an immunosuppressive drug, and can also bind non-specifically to other cyclophilins, therefore causing off-target effects. Inhibition of CypD expression using siRNA has been examined as a potential cardioprotective therapy (Kato et al., 2009, Cardiovasc. Res. 83:335-344). However SMOs have a therapeutic advantage over siRNA in that unlike siRNA, SMOs do not affect transcript degradation through recruitment of RNAase H which can cause immune reactions and other off target effects.
There is presently no known cure for PWS, ALS, AD or any of a number of other diseases that result from aberrant pre-mRNA splicing. There is a need in the art for the development of more selective and efficacious therapeutic agents for the treatments of various diseases and conditions affected or mediated by 5HT2CR, GluRs, OGA, Aph1B, FOXM1, ERBB3, and CypD. In addition, there are a number of diseases where altering pre-mRNA splicing may have a positive therapeutic effect even when that gene is not directly affected by the pathogenesis of the disease. Accordingly, there is an urgent need in the art for compositions and methods related to pre-mRNA splicing as it affects various diseases and disorders. The present invention fills this need.